Fuel injectors for gas turbine engines on an aircraft direct fuel from a manifold to a combustion chamber. The fuel injector typically has an inlet fitting connected to the manifold for receiving the fuel, a fuel spray nozzle located within the combustion chamber of the engine for atomizing (dispensing) the fuel, and a housing stem extending between and supporting the fuel nozzle with respect to the fitting. Appropriate check valves and/or flow dividers can be disposed within the fuel nozzle to control the flow of fuel through the nozzle. The fuel injector is typically heatshielded to protect the injector from the high operating temperatures within the engine casing. Multiple injectors can be attached to the combustor casing of the engine in a spaced-apart manner to dispense fuel in a generally cylindrical pattern.
Fuel conduit(s) are provided through the housing stem, and direct fuel received in the fitting into the upstream end of the nozzle. As illustrated in FIG. 1, in a prior art dual-flow system (i.e., with primary and secondary flows), a primary adapter 10 is provided centrally within the nozzle 12 and fuel is directed downstream within the nozzle in two passageways. A first (inner) passageway 14 is provided centrally within the adapter and fluidly interconnects a first fuel conduit 16 in the housing stem 18 with a first, central discharge orifice 20 at the discharge end of the nozzle. A second (outer) passageway 22 is provided between the outer surface of the adapter and a heat shield/fuel conduit portion 24 surrounding the adapter, and fluidly interconnects a second fuel conduit 26 in the housing stem with a second, annular discharge orifice 28 at the discharge end of the nozzle, with the second discharge orifice 28 having a generally annular configuration concentrically surrounding the first discharge orifice 20. At the downstream end of the nozzle, geometry (such as swirler vanes 30) may be provided in the first and/or second passageways to impart a swirling component of motion to the fuel. The fuel sprays are applied to a prefilmer 31, and directed outwardly from the discharge end of the nozzle in a conical spray of fuel. The swirling spray is ignited downstream of the nozzle in the combustor.
While the nozzle design described above has been used for many years and provides a satisfactory fuel spray, one aspect of such a design is that the fuel flow must turn a sharp ninety degrees from the fuel conduits in the housing stem to the fuel passageways in the nozzle, and is directed into the second (outer) passageway through an opening 32. Opening 32 is located toward the upper portion of the passageway, and is sometimes kidney-shaped. As can be appreciated, as the fuel is directed into the annular, outer passageway 22 from the opening 32, there is a sudden expansion of the flow path. At low or moderate fuel flow rates and pressures typical of start-up and cruise conditions, the fuel entering the second passageway tends to be directed to the upper (12 o'clock) portion of the annulus. The fuel then tends to flow axially and (somewhat) circumferentially/azimuthally downstream in the passageway, however the greater volume and density of fuel remains in the upper portion of the passageway all the way to the discharge orifice, and recirculation zones form in the passageway annulus at the opposite (6 o'clock) location. The recirculation zones are detrimental for total-pressure loses and heat transfer in the nozzle, as they increase the fuel residence time in the nozzle. The propensity for carbon formation (coking) in this region also increases. The spray from the nozzle also tends to have non-uniform distribution of fuel, which decreases the efficiency of combustion and the stability of the flame. At high power (take-off) conditions, the fuel is highly turbulent and so these effects are somewhat reduced—but they are still an issue.
Referring to FIG. 2, it is known to provide an annular flange 34 at the upstream end of the adapter having a dimension slightly smaller than the inner dimension of the surrounding fuel conduit 36. An arcuate or wedge-shaped portion (indicated generally at 37) of the flange is removed, with the removed portion being located approximately 180 degrees from the inlet opening 32. When the fuel enter the upstream end of the passageway, some of the fuel is forced to flow to the opposite side of the passageway before it can flow across the flange, which thereby causes more uniform distribution of the fuel around the passageway. It is necessary to rotationally orient (“clock”) the adapter in the nozzle during assembly such that the removed portion is properly rotationally oriented with respect to the inlet opening. As can be appreciated, this requires additional cooperating structure between the adapter and nozzle, and complicates the manufacturing and assembly process.
It is noted this design includes an annular shoulder 38 downstream of the flange; however it is believed the shoulder is used primarily to facilitate atomization of the fuel because of its location downstream along the adapter. The shoulder also has a relatively sharp edge, and if the edge is located too close to the surrounding fuel conduit, the edge can cause fuel separation and high pressure drop. Thus, it is believed the shoulder in this nozzle design is not intended to provide significant fuel distribution around the circumference of the passageway, beyond what is provided by the upstream flange.
Thus it is believed there is a demand in the industry for a further improved fuel injector for gas turbine engines, and particularly for an improved nozzle for such an injector, which provides a substantially uniform spray for efficient combustion and stability of the flame, and which reduces the complexity (and cost) of manufacture and assembly of the nozzle.